The regulation of the uterine blood flow is being investigated in near-term sheep. We are testing the hypothesis that the uterine blood flow is regulated by and dependent on the umbilical blood flow. We therefore believe that uterine vascular insufficiency may be a fetal deficit rather than a deficiency of the maternal organism. We are examining the local response of the uterine blood flow to ligation of part of the umbilical vascular tree and to changes in the umbilical blood flow induced by changes in fetal blood volume. Time courses of the response are being examined. Changes are being observed using radioactive microspheres injected at various intervals after the surgery and with electromagnetic flow meters. The undersigned agrees to accept responsibility for the scientific and technical conduct of the project and for provision of required progress reports if a grant is awarded as the result of this application.